Microwave-Assisted Synthesis of NiCo2O4 Double-Shelled Hollow Spheres for High-Performance Sodium Ion Batteries
Nano-Micro Lett.
Microwave-Assisted Synthesis of NiCo2O4 Double-Shelled Hollow Spheres for High-Performance Sodium Ion Batteries
Xiong Zhang 0 1
. Yanping Zhou 0 1
. Bin Luo 0 1
. Huacheng Zhu 0 1
. Wei Chu 0 1
. Kama Huang 0 1
0 School of Electronics and Information Engineering, Sichuan University , Chengdu 610065 , People's Republic of China
1 School of Chemical Engineering, Sichuan University , Chengdu 610065 , People's Republic of China
The ternary transitional metal oxide NiCo2O4 is a promising anode material for sodium ion batteries due to its high theoretical capacity and superior electrical conductivity. However, its sodium storage capability is severely limited by the sluggish sodiation/desodiation reaction kinetics. Herein, NiCo2O4 double-shelled hollow spheres were synthesized via a microwave-assisted, fast solvothermal synthetic procedure in a mixture of isopropanol and glycerol, followed by annealing. Isopropanol played a vital role in the precipitation of nickel and cobalt, and the shrinkage of the glycerol quasi-emulsion under heat treatment was responsible for the formation of the double-shelled nanostructure. The as-synthesized product NiCo DH glycerol qausiemulsion initial annealing
NiCo2O4; Double-shelled hollow sphere; Microwave; Sodium ion battery
Highlights
NiCo2O4 double-shelled hollow spheres were successfully synthesized via a rapid microwave-assisted solvothermal
method in isopropanol with the aid of glycerol.
The roles of isopropanol, nitrate, glycerol, and the heating rate in the formation of the double shelled hollow spheres
were systematically studied.
The as-synthesized NiCo2O4 double shelled hollow spheres showed good sodium storage performance with reversible
specific capacity of 511 mAh g-1 at 100 mA g-1.
glycerol
further
anneaing
microwave
glycerol
shrinkage
NiCo2O4 DSHS
NiCo2O4 yolk shell
NiCo2O4 shell
was tested as an anode material in a sodium ion battery,
was found to exhibit a high reversible specific capacity of
511 mAh g-1 at 100 mA g-1, and deliver high capacity
retention after 100 cycles.
1 Introduction
Presently, due to increasing energy consumption, there is
an increasing demand for energy storage materials. Lithium
ion batteries (LIBs) offer high energy storage density, long
cycling life, and excellent safety properties, thus
dominating the market for portable electronic device power
sources [
1
]. However, the depletion of lithium resources
and the consequent high cost of lithium hinder the
application of LIBs in several emerging areas, such as
largescale grid energy storage [
2
]. Sodium, another Group I
element, is much more abundant and has a much lower
cost. As such, sodium ion batteries (SIBs), which have a
charging/discharging mechanism similar to that of LIBs,
are promising energy storage devices for the future and
have received great research attention in the past few years
[
3
]. Nevertheless, the energy storage performance of SIBs
is significantly limited by a lack of suitable electrode
materials. For example, while graphite is used as the anode
material in most commercial LIBs, it is nearly
electrochemically inactive with sodium due to the large ionic
radius of Na? [
4
]. Although many other carbonaceous
materials have been intensively investigated as anode
materials for SIBs, their sodium storage capabilities are too
low to meet the demands of practical applications.
Transitional metal oxides have been widely investigated
as substitutes for carbonaceous anode materials in LIBs [
5
].
In particular, ternary transition metal oxides such as
NiCo2O4 are extremely attractive, due to their high
theoretical storage capacities (e.g., 890 mAh g-1 for NiCo2O4
compared to 372 mAh g-1 for graphite) and superior
electrical conductivity (2 orders higher than that of
singlecomponent cobalt or nickel oxides) [
6
]. Theoretically,
NiCo2O4 has equivalent storage capacities for both sodium
and lithium. Recently, some work has been reported on the
successful application of NiCo2O4 as an anode material for
SIBs [
7, 8
]. However, due to the sluggish
sodiation/desodiation reaction kinetics, as well as the large volume
change during the charging/discharging process induced by
the large ionic radius of Na?, the reported NiCo2O4
materials exhibit greatly inferior capacities for sodium
storage. In order to increase the practical sodium storage
capacity of this material, a new strategy to engineer robust
nanostructured NiCo2O4 is urgently needed. One attractive
avenue amongst the various approaches is the use of
hollow multi-shelled spheres, due to their unique structural
features [
9–17
].
Recently, microwave-assisted nanotechnology has
attracted a great deal of research interest, due to the interest
in green chemistry in both academia and industry.
Microwaves heat the reactants directly via dielectric loss, rather
than by heat convection as in the conventional heating
method. This unique heating mechanism allows the use of
microwaves to gr (...truncated)